This invention relates to aircraft speedbrakes, and in particular to speedbrakes which are stored in some portion of the aircraft other than its wing and which do not affect the aerodynamics of the wing when deployed.
With general aviation aircraft it is difficult to descend rapidly without either shock cooling the engines, overspeeding the airframe or both. This is because this class of aircraft is not designed for rapid descent and achieving it requires operating the aircraft outside of its normal operating envelope. One way to achieve a high descent rate in general aviation aircraft is to reduce the power level until it is at or near idle. However, the engines used in this type of aircraft are air cooled and are designed to maintain design operating temperature at altitude when operating at cruise power. Thus, at lower power settings the engines do not produce enough energy to keep them warm. Another way to achieve rapid descent is to maintain cruise, or near cruise, power, thereby preventing shock cooling, but fly at a negative angle of attack. Doing so increases the speed of the aircraft, however, and its speed will exceed design limits before high descent rates are achieved.
While speedbrakes have commonly been used to reduce the speed of an aircraft, and thus increase its rate of descent, without having to reduce power or angle of attack, the speedbrakes of the prior art have had inherent difficulties which have limited their acceptance on general aviation aircraft. Heretofore, speedbrakes have been part of the wing or have been associated with the wing. As a result they affect the aerodynamic characteristics of the wing when deployed. Typically, wing-mounted speedbrakes alter the pitch of the aircraft whenever they are extended or retracted, thereby requiring the pilot to retrim the aircraft. Many general aviation pilots find this objectionable, and, for novice pilots, it can be dangerous. This is particularly true when a landing is being made with the speedbrakes extended and it is necessary to abort the landing close to the ground.
In addition, wing-mounted speedbrakes are difficult to retrofit into existing aircraft. This is because the wings typically contain the fuel tanks and are difficult to obtain access to for locating the actuation mechanism and control cables. Because the necessity for having speedbrakes in general aviation aircraft has recently become acute, due to increased airport utilization which requires rapid descent from high altitude during landing, the ability to retrofit it on existing aircraft has become an important aspect of any speedbrake system.
Finally, the prior art wing-mounted speedbrakes are deployed against the airstream and thus transmit the aerodynamic loads generated on them through their actuation system. As a result, the actuation system must be large and quite heavy and must have enough power to overcome the aerodynamic loads. In addition, the mounting structure for the actuators must be heavy in order to transmit this concentrated load to the aircraft structure.
The present invention overcomes the foregoing shortcomings and limitations of prior art speedbrakes by installing them in the engine nacelles, behind the trailing edge of the wing and by making them translate laterally between their extended and retracted positions.
Each speedbrake is carried by a support frame which allows it to be installed as a unit into the nacelle. In the preferred embodiment, the speedbrake is installed into the baggage compartment which further eases its installation as a retrofit in an existing aircraft. A flap, slidably mounted in the frame, translates between a retracted position in the nacelle and an extended position outboard of the nacelle and aft of the trailing edge of the wing. The flap comprises a U-shaped housing which has elongate track sections extending outwardly from its lower extremities. The track sections have V-shaped edges which are engaged in V-shaped grooves in spaced-apart sets of rollers which are mounted on the support frame. Thus, the track and rollers form a slide mechanism which permits the housing to translate freely into and out of the nacelle. This slide mechanism then transmits all of the aerodynamic load of the flap to the aircraft structure so that none of this load is imparted to the flap actuation system. Thus, the load is spread over a large contact area and hard points are not required to receive concentrated loads through the actuator as is the case with the prior art speedbrakes.
Located in the housing are four plates which are mounted on pivots that allow them to be rotated up into the housing or extend down from it. The plates are arranged in two pairs with each pair including a plate which rotates outwardly and a plate which rotates inwardly, with the plates in each pair being interconnected by a lever which causes them to rotate in unison. A low-friction striker plate is mounted in the nacelle at a location where it will contact the outwardly rotating plates as the housing is retracted into the nacelle and rotate them up into the housing. Thus, the plates are withdrawn into the housing automatically as the flap is retracted and are extended from the housing automatically as the flap is extended.
The flap located in one of the two engine nacelles has a motor which moves it between its extended and retracted positions and the flap located in the other engine nacelle is connected to the motor-driven flap by a cable system. The motor is actuated by a switch located in the cockpit. The switch permits the flaps to be extended in any incremental amount desired, but causes them to be fully retracted when any retraction is initiated. Because the aerodynamic load generated on the flap is transmitted to the aircraft through the track and rollers, the motor and cable system can be quite lightweight. In addition, the motor can be relatively low powered. Thus, these components can be relatively lightweight and inexpensive.
Since the flaps are located behind the trailing edge of the wing they do not affect the aerodynamic performance of the wing. By translating between their extended and retracted position, rather than rotating as is the case with prior art flaps, it is possible to position the flaps in the desired location and to arrange them so that their vertical extent is greater when they are extended than when retracted.
Accordingly, it is a principal object of the present invention to provide speedbrakes which do not influence the aerodynamic performance of the wing when they are extended.
It is a further object of the present invention to provide such speedbrakes which deflect thrust as well as increase drag.
It is a further object of the present invention to provide speedbrakes which have greater vertical extent when extended than when retracted.
It is a still further object of the present invention to provide speedbrakes which are extended and retracted by being translated parallel to their planar face.
It is a yet further object of the present invention to provide speedbrakes which are not stored in the wing of the aircraft.
The foregoing and other objectives, features and advantages of the present invention will be more readily understood upon consideration of the following detailed description of the inventi speedbrake when deployed, with the nacelle in which it is placed being shown in section.
FIG. 3 is a fragmentary sectional view taken along the line 3--3 in FIG. 2.
FIG. 4 is a fragmentary sectional view taken along the line 4--4 in FIG. 2.
FIG. 5 is a sectional view taken along the line 5--5 in FIG. 4.